The U.S. Department of Justice (DOJ) has launched a sweeping investigation into Americans who have worked with Russian state television. This move is part of a major effort to stop Russia’s influence in the upcoming presidential election in November.

This month, F.B.I. agents raided the homes of two well-known figures connected to Russian state media: Scott Ritter, a former U.N. weapons inspector and critic of U.S. foreign policy, and Dimitri K. Simes, a former adviser to Donald Trump’s ...